A display device having an active-matrix substrate has been known. In the processing for manufacturing an active-matrix substrate, contacting, friction, and peeling frequently occur between a glass substrate and another material. For that reason, the accumulation of an electrical charge on a semiconductor layer, scanning lines, and signal lines or the like on the glass substrate is unavoidable, and static electricity could break down thin-film transistors (abbreviated TFTs hereinafter) or interconnects.
A method of manufacturing an active-matrix type liquid crystal display device is disclosed in Patent Document 1 noted below as a method of preventing the phenomenon of breakdown caused by this type of static electricity. Patent Document 1 describes a surge protection circuit that prevents breakdown of elements in a liquid crystal panel by the application of a surge voltage.